Fix listobjects with metadata

`UserMetadata` did not match actual format sent.
Change type of `UserTags`, so it can be unmarshaled from XML.

Fix for minio server that matches this will be sent.

Tested with mc.

api-datatypes.go

@@ -43,14 +43,29 @@ type StringMap map[string]string
 // if m is nil it can be initialized, which is often the case if m is
 // nested in another xml structural. This is also why the first thing done
 // on the first line is initialize it.
-func (m *StringMap) UnmarshalXML(d *xml.Decoder, _ xml.StartElement) error {
+func (m *StringMap) UnmarshalXML(d *xml.Decoder, s xml.StartElement) error {
 	*m = StringMap{}
-	type Item struct {
-		Key   string
-		Value string
-	}
 	for {
-		var e Item
+		// Fallback for <key>value</key>
+		if s.Name.Local == "UserMetadata" {
+			var e struct {
+				XMLName xml.Name
+				Value   string `xml:",chardata"`
+			}
+			err := d.Decode(&e)
+			if err == io.EOF {
+				break
+			}
+			if err != nil {
+				return err
+			}
+			(*m)[e.XMLName.Local] = e.Value
+			continue
+		}
+		var e struct {
+			Key   string
+			Value string
+		}
 		err := d.Decode(&e)
 		if err == io.EOF {
 			break
@@ -124,7 +139,7 @@ type ObjectInfo struct {
 	UserMetadata StringMap `json:"userMetadata,omitempty"`
 
 	// x-amz-tagging values in their k/v values.
-	UserTags map[string]string `json:"userTags"`
+	UserTags StringMap `json:"userTags" xml:"TagSet"`
 
 	// x-amz-tagging-count value
 	UserTagCount int